The invention relates generally to blood pressure measuring equipment and to improvements therein.
The prior art is replete with devices for measuring the blood pressure of a living subject. An old and simple device is a pressurizable cuff used in combination with a mercury manometer which reads pressure in the cuff and a stethoscope which is used to listen to Korotkoff sounds. More complicated methods and apparatus using the same principle of listening to the Korotkoff sounds replace the mercury manometer with a mechanical or electromechanical pressure gauge and utilize microphonic detection of the Korotkoff sounds which are analyzed electrically.
Oscillometric methods for determining blood pressure are also well known in the art. In such methods, a representation of the strength of pulsations of pressure within an artery are observed either by an operator or by electronic signal processing means. Various techniques for determining blood pressure, systolic and/or diastolic, have been disclosed in U.S. Pat. No. 3,903,872 issued Sept. 9, 1975 to William T. Link for Apparatus and Process for Producing Sphygmometric Information, and in U.S. patent application Ser. No. 578,074 filed May 15, 1975 by Link et al for Apparatus and Process for Determining Systolic Pressure, which patent and application are respectively incorporated herein by reference.
The techniques disclosed in the aforementioned Link patent and Link et al patent application provide objective and relatively accurate means for the determination of diastolic and/or systolic blood pressure and utilize a signal obtained from a pressure cuff for the subsequent oscillometric waveform analysis. The signal obtained from the pressure cuff is representative of a sum quantity, S, comprised of the selectively changeable pressure, P.sub.dc, applied by the cuff externally adjacent the blood vessel and a time dependent fluctuating component, P.sub.ac, representative of the pulsatile pressure within the blood vessel. This sum quantity is analyzed in accordance with one or more predetermined algorithms for determining diastolic and/or systolic pressure within the blood vessel. In accordance with various preferred algorithms, particularly as disclosed in the aforementioned Link patent and Link et al patent application, the time dependent fluctuating component P.sub.ac or a time derivative thereof comprises the signal analyzed by the algorithm for determining diastolic and/or systolic pressure.
In those foregoing instances in which the fluctuating component P.sub.ac of the measured sum quantity is utilized by the analytical algorithm, it is generally required that the fluctuating component P.sub.ac be separated by a filter network from the sum value S for the purpose of the subsequent analytical determination. This separation may in fact comprise a first time differentiation of the fluctuating component and indeed even a second time differentiation in certain instances where required. Thus, it will be appreciated that such time differentiations of the fluctuating signal P.sub.ac may be accomplished by filtering networks having predetermined AC time constants which also serve to separate the P.sub.ac component from the sum quantity S.
During start-up of the blood pressure measuring apparatus various transient signals may be generated which, due to the AC time constants of the filter networks and other preceding circuitry, may continue to exist even after completion of the start-up interval. These transient signals may have AC characteristics similar to those of the P.sub.ac fluctuating signal which comprises the principle informational input to the analytical processing circuitry, and thus may distort the informational input during the early stages of a blood pressure measurement run.
Accordingly, it is a principle object of the invention to provide new and improved blood pressure measuring apparatus.
It is a further object of the invention to provide new and improved blood pressure measuring apparatus which minimizes erroneous pressure data readings during and shortly after start-up conditions.